1. Field of the Invention
The present invention relates to a display apparatus as well as a signal processing apparatus for a display apparatus that is suitable for application to a large image plane/highly accurate display apparatus such as a liquid crystal display and a projector, etc.
2. Related Background Art
Advent of the multimedia age brings display apparatus to all the scenes, and since projection type display apparatus is efficient compared with other systems in particular, front projectors are in common use for presentations, etc. and rear projectors are in common use for domestic theaters.
In recent years, CRT projection is being replaced by a projector in a liquid crystal panel system and a DMD (digital mirror device, for which reference should be made to Japanese Patent Application Laid-Open No. 10-78550) method modulating light quantity by changing angles of an mirror which are turning to spread because they are appropriate for providing high luminance and highly delicate accuracy.
However, these projection-type display apparatuses is inferior to CRT display tubes in general use in terms of picture quality, and for high picture quality display (display demanded for quality feeling), users tend to use CRT display tubes even when the image plane size is small. High picture quality (quality feeling) herein referred to is high dynamic range (capability of high contrast and high gradation display).
Since a CRT, luminance of which can be modulated with electron beam intensification, etc., dynamic range can realize up to around 1000:1 in the case where only a particular range (a partial region) displays white, etc. Accordingly, its potentiality can make white brighter and black darker to realize excellent picture quality. However, in case of a CRT system, the size thereof is around 40 inches at largest due to limitation in a tube, etc., giving rise to a problem that there exists a high degree of technological difficulty for larger sizes.
On the other hand, in a projection-type display apparatus, a CRT system is traded off in terms of its engine size, brightness and high accuracy, etc, and as described above, a liquid crystal system as well as a DMD system is suitable for high luminance and high accuracy is recently in a main stream. In these cases, the liquid crystal and the DMD are assigned to play roles of a light modulator, and a lamp illuminates the above described liquid crystal device or DMD to be enlarged for projection by a projection optical system. Accordingly, the above described dynamic range is determined wit the dynamic range mainly provided by the liquid crystal device or DMD.
The practical dynamic range of the above described device is approximately 300 to 400:1 for liquid crystals and approximately 500 to 600:1 for DMDs. Accordingly, they used to have a problem that there is a long way to win against the above described CRT system in terms of one point of high picture quality (high dynamic range).
In addition, a direct-view-type LCD likewise used to have a problem that its dynamic range is low, compared with the CRT.
Incidentally, as background documents of the present application, Japanese Patent No. 2643712, Japanese Patent Application Laid-Open No. 6-102484 and Japanese Patent Application Laid-Open No. 11-65528 and Japanese Patent Application Laid-Open No. 6-167717 are nominated.